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The international journal for inorganic, organometallic and bioinorganic chemistry
Paper
Dalton Trans., 2006, 237 - 249, DOI: 10.1039/b513107c
Copolymerization of cyclohexene oxide and carbon dioxide using (salen)Co(III) complexes: synthesis and characterization of syndiotactic poly(cyclohexene carbonate)
Claire T. Cohen, Christophe M. Thomas, Kathryn L. Peretti, Emil B. Lobkovsky and Geoffrey W. Coates
Synthetic routes to a series of new (salen)CoX (salen = N,N
-bis(salicylidene)-1,2-diaminoalkane; X = halide or carboxylate) species are described and the X-ray crystal structures of two (salen- 1)CoX (salen- 1 = N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminocyclohexane; X = Cl, I) complexes are presented. (R,R)-(salen- 1)CoX (X = Cl, Br, I, OAc, pentafluorobenzoate (OBzF5)) catalysts are active for the copolymerization of cyclohexene oxide (CHO) and CO2, yielding syndiotactic poly(cyclohexene carbonate) (PCHC), a previously unreported PCHC microstructure. Variation of the salen ligand and reaction conditions, as well as the inclusion of [PPN]Cl ([PPN]Cl = bis(triphenylphosphine)iminium chloride) cocatalysts, has dramatic effects on the polymerization rate and the resultant PCHC tacticity. Catalysts rac-(salen- 6)CoX (salen- 6 = N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-diaminopropane; X = Br, OBzF5) have high activities for CHO/CO2 copolymerization, yielding syndiotactic PCHCs with up to 81% r-centered tetrads. Using Bernoullian statistical methods, PCHC tetrad and triad sequences were assigned in the 13C NMR spectra of these polymers in the carbonyl and methylene regions, respectively.
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